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Topic: Basic question about storing an object (Read 973 times) previous topic - next topic


Hey guys,

I'm a bit confused what's the best way to store my sensors name. I'd really appreciate any information about what I am misunderstanding. My problem is that I run into a memory issue and I try to improve the memory usage - so I thought lets begin with the strings. The name of the sensor is used to identify it in debug-messages.

With either option 1a or option 1b (no option 2, no option 3, no option 4) my Arduinos RAM is used with 9 Bytes (some default stuff), I'm fine with that.

  • The combination of 1a and 3 still uses 9 Bytes. I'm wondering why it is not 9 + 4x2B (for 2B/int) = 17B because it is in global scope?
  • Adding option 4 I was expecting 17B + 10x1 (1B/char) = 27B - but it's still 9B?
  • Adding option 2a results in 33B - why?! I still expected 27B.
  • Changing 1a to 1b results in 15B, but I expected either 9B (only for the default stuff) or 14B (for copying the value -> 9 + 4x1 (1B/char from "name") + 1B (for zero-terminating of "name") - why?
  • One more point: Changing now 2a to 2b still uses 15B (also 15B is the result when changing 2a to 2b in list-step 3) - I don't get it?

Code: [Select]
class cClass {
  void setName(const char* sensorName) {
    // Option 2a
    //strcpy(sName, sensorName);
    // Option 2b
    //EEPROM.put(0, sensorName);
  const char sName[10];

  // Option 3
  int a;
  int b;
  int c;
  int d;


// Option 1a
 cClass newC;
void setup() {
  // Option 1b
  //cClass newC;

void loop() {

Many thanks in advance and best regards


I'm having trouble understanding your issue, but I doubt that you're likely to have enough sensors that giving each of them a ten byte name is going to kill your RAM usage. Post your code so we can look for other places to save.


Mar 24, 2020, 03:39 pm Last Edit: Mar 24, 2020, 04:07 pm by alve89
Thank you for your quick response!
If I'd post my complete code, I'd post about 3.000 lines of code - that's not the best way to search the problems, I think.   :) I'm beginning at the smallest / first point where my memory usage could be reduced - and that's the way to store my objects. But obviously I have problems understanding the way the storing works as you can see in my example code - I am expecting different value than those really come true at the end of compiling. To really solve my memory issue I need to find my misunderstanding of memory usage in general - do you agree with that?  :smiley-confuse:

But as I am very happy about every helpful support I give you the link to the Git instead of posting the code: https://github.com/alve89/growbox

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